Theory of single spin inelastic tunneling spectroscopy

TL;DR

This paper develops a phenomenological model to describe inelastic tunneling spectroscopy of single spins, explaining experimental observations of spin excitations in magnetic atoms and chains via a spin-assisted tunneling Hamiltonian.

Contribution

It introduces a new theoretical framework linking inelastic STM spectra to spin spectral weight, capturing experimental features like spin selection rules and odd-even effects.

Findings

The theory matches experimental data for Fe and Mn atoms.

It explains the spin selection rules in inelastic tunneling.

Accounts for magnetic anisotropy and odd-even effects in spectra.

Abstract

Recent work shows that inelastic electron scanning tunneling microscope (STM) probes the elementary spin excitations of a single and a few magnetic atoms in a thin insulating layer. Here I show that this new type of spectroscopy is described using a phenomenological spin-assisted tunneling Hamiltonian. Within this formalism, the inelastic $dI/dV$ lineshape is related to the spin spectral weight of the probed magnetic atom. This accounts for the spin selection rules observed experimentally. The theory agrees well with existing STM experiments for single Fe and Mn atoms as well as linear chains a few Mn atoms. The magnetic anisotropy in the inelastic $dI/dV$ and the marked odd-even $N$ effects are accounted for by the theory.